1. Field of the Invention
The present invention relates to a patch radiating antenna array, specifically an array utilizing groupings of high frequency patches, closely spaced to produce simultaneously a low frequency array.
2. Description of the Prior Art
It is often advantageous to radiate or receive two or more radio frequencies from a single antenna. If that antenna is to also be a phased array antenna it is also advantageous that the antenna be very thin.
Patch radiators used in arrays, such as microwave or millimeter wave power radiating elements, are a well established means of achieving planar, thin printed circuit antennas.
However, several problems result when patch radiating elements operable to radiate at two distinct RF frequencies are used on the same array. First, the maximum spacing between the phased patch radiating elements is different for two distinct transmitted frequencies. A high frequency spacing of the patch radiating elements may be less than the minimum practical radiating element size for the low frequency patch radiating element spacing.
Second, widely spaced, low frequency patch radiating elements tend to cause interference lobes in the high frequency transmission patterns of high frequency patch radiating elements.
Thirdly, the physical inter-fitting of occasional low frequency patch radiating elements in the limited space between high frequency patch radiating elements results in a very narrow bandwidth for the emitted signal. Finally, most low frequency patch radiating elements are physically large requiring an extensive surface area.
The U.S. Pat. No. 4,450,449, issued May 22, 1984 to Harold S. Jewitt, entitled "Patch Array Antenna" addressed the need in this area for a multi-frequency array antenna. The patent to Jewitt discloses the use of separate substrate layers etched to produce two individual and distinct patch arrays. These two distinct arrays do not function in a complementary manner and are merely blended together so that the patches of the rear array are behind the open spaces of the front array. For multiple frequency antennas the Jewitt design requires that one array radiate at a first frequency, in a configuration optimally designed for that frequency, while the other array radiates at, and is designed for, a second distinct frequency.
The Jewitt array comprising two distinct non-complementary, radiating systems sharing the same ground plane does not lend itself to effective function as a scanning array radiating antenna. In the frequency scanning mode the patch radiating elements would be farther apart on the array resulting in grading lobes and signal interference.
The problem to be solved therefore is multiple radio frequency power transmission in the low and high frequency range, where for this application the low frequency range is UHF and the high frequency range is the S-band, utilizing high frequency patch radiating elements grouped together and functioning as low frequency patch radiating elements to achieve effective multi-frequency antenna array operation.